Technical Field
The present disclosure relates to systems and methods for controlling an electrosurgical generator. In particular, the present disclosure relates to an electrosurgical generator including an active clipper circuit for controlling a crest factor of a radio frequency waveform generated by a power converter.
Background of Related Art
Electrosurgery involves application of electrical energy to a surgical site to cut, ablate, desiccate, or coagulate tissue. In monopolar electrosurgery, a source or active electrode delivers electrical current from an electrosurgical generator to targeted tissue. A patient return electrode is placed remotely from the active electrode to conduct the current back to the generator.
In bipolar electrosurgery, return and active electrodes are placed in close proximity to each other such that an electrical circuit is formed between the two electrodes (e.g., in the case of an electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes. Accordingly, bipolar electrosurgery generally involves the use of instruments where it is desired to achieve a focused delivery of electrosurgical energy between two electrodes.
Conventional electrosurgical generators rely on output filtering to shape the waveform of the power output by the generator. Electrosurgical generators may include alternating current (“AC”) power converters, which generate substantially sinusoidal waveforms at predetermined frequencies. In conventional electrosurgical generators, it is known to adjust a crest factor of an electrosurgical waveform to control tissue effect. Crest factor is a ratio of peak voltage value to root mean square (“RMS”) value of the waveform. Thus, for example, a pure square waveform has a crest factor of about 1 and a pure sinusoidal waveform has a crest factor of about 1.414, since the peak of a true sinusoid is 1.414 times its RMS value.
Conventional electrosurgical generators may also include resonant output filters to produce sine wave waveforms from RF converters. Thus, these generators operate at a single frequency and rely on the filtering to remove unwanted harmonics. The crest factor of a filtered output may be changed using time domain manipulation such as duty cycle modulation (e.g., by sending out a short burst of pulses). However, there are several drawbacks and limitations to the performance of the conventional resonant devices. Crest factor control is significantly limited by characteristics of the hardware filters since these filters only work over a very limited frequency range or a fixed frequency and crest factor changes dramatically for a given duty cycle with variations in load impedance. Duty cycle modulation produces many subharmonic frequencies, which can contribute to electromuscular stimulation. Furthermore, crest factors below 1.4 are not achievable using generators including resonant networks.
Accordingly, there is a need for new and improved systems and method for controlling electrosurgical generators, which are not limited to any particular narrow frequency range and do not require output filtering to achieve reasonable power output.